Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:                AP access point        BS base station        DIUC downlink interval usage code        DL downlink        HO handover        MRS (M-RS) mobile RS        MS mobile station        OFDM orthogonal frequency division multiplex        RS relay station        SS subscriber station        UE user equipment        UL uplink        WiMAX world interoperability for microwave access (IEEE 802.16)        
A wireless relay network is a multi-hop system in which end nodes (UE/MS/SSs, referred to for convenience hereafter as UEs) may be connected to the BS or AP via a RS. UL or DL traffic between UEs and the BS/AP may pass through and be processed by the RS. An example of a relay network concept is described in IEEE 802.16 Multi-hop Relay (MR), which is a newly established task group that is referred to as 802.16j. The MR effort is focused on defining a network system that uses RSs to extend the network coverage and/or enhance the system throughput.